1. Field of the Invention
The present invention relates to an exhaust pipe assembly which is suitable for connection between an exhaust manifold of a multi-cylinder internal combustion engine of a motor vehicle and a catalyst converter. In particular, it relates to an exhaust pipe assembly employing a two-passage construction in general in which a so-called "THgr" pipe, whose exhaust passage is divided into two by a partition plate, is used in order to prevent the exhaust interference among the cylinders. It also relates to an exhaust pipe assembly employing a double-pipe construction in order to prevent the exhaust gas from lowering in temperature before it reaches a catalytic converter and to prevent personal harms due to high temperature.
2. Description of Related Art
In order to prevent the exhaust interference among the cylinders and to prevent the heat dissipation, an exhaust pipe assembly of two-passage and double-pipe construction is known, for example, from Published Unexamined Japanese Patent Application No. 192727/1997. This kind of conventional exhaust pipe assembly as shown by reference alphabet E in FIG. 10A is connected to a flange f2 of an exhaust manifold M of a multi-cylinder internal combustion engine (not illustrated). The exhaust pipe assembly E is made up of an inner pipe xe2x80x9caxe2x80x9d and an outer pipe b which are welded to a flange f1. A partition plate c is elongated in a longitudinal direction of the inner pipe xe2x80x9caxe2x80x9d so as to form two exhaust passages g1, g2 divided along the diameter of the inner pipe xe2x80x9ca.xe2x80x9d A thermally insulating space e is provided between the periphery (i.e., outer surface) of the inner pipe xe2x80x9caxe2x80x9d and the inner circumference of the outer pipe b. The partition plate c is, in most cases, welded by laser beam welding to an extended piece c1 from an outside. A small curvature R is formed at a base portion of that partition plate c which comes into contact with the extended piece c1 to facilitate the deformation of the partition plate c. The thermal expansion is thus absorbed by the extended piece c1 which is provided on each of the diametrically opposite ends.
That portion of the partition plate c which lies on the side of the flange f1 is exposed most frequently to the high-temperature exhaust gas as compared with a portion of the inner pipe xe2x80x9caxe2x80x9d and the flange f1, whereby a maximum thermal expansion occurs therein. However, the portion in question of the partition plate c is welded to a slip-on or inserting hole of the flange f1 together with the inner pipe xe2x80x9caxe2x80x9d and is therefore restricted in its expansion in the diametrical direction. Therefore, the partition plate c gives rise to buckling and deformation, as shown by dotted lines in FIG. 10B, and the exhaust passages g1, g2 are subject to changes in shape. As a result, there is a possibility that the exhaust passages in the exhaust pipe assembly E differ from those in the exhaust manifold M. In addition, when the welded portions in the extended pieces c1 try to be displaced as a result of the deformation in the partition plate c, the inner pipe xe2x80x9caxe2x80x9d cannot follow the deformation. The welded portion thus sometimes gives rise to peeling, with the resultant poor sealing effect. Further, as a result of repeated bending loads due to thermal expansion and contraction, the welded portion may give rise to fatigue rupture and the partition plate c may be damaged due to fatigue. In any of the above-described cases, the engine output and the torque decrease.
In view of the above points, the present invention has an object of providing an exhaust pipe assembly of two-passage construction.
In order to attain the above and other objects, according to one aspect of the present invention, there is provided an exhaust pipe assembly of two-passage and double-pipe construction, comprising: an inner pipe; a partition plate meeting the inner pipe at both diametrical meeting ends thereof so as to be elongated in a longitudinal direction of the inner pipe, whereby two passages divided across a diameter of the inner pipe are formed; an outer pipe covering the inner pipe with a thermally insulating space around a periphery of the inner pipe, the outer pipe having on one longitudinal end thereof a connecting portion for connection with a mating member, wherein one end of the inner pipe is fixedly connected to the outer pipe with a clearance between the periphery of the inner pipe near each of the meeting ends and an inner circumference of the outer pipe.
Preferably, the exhaust pipe assembly further comprises a connecting member provided at the connecting portion, for connecting the exhaust pipe assembly to the mating member.
The inner pipe at the connecting portion is preferably formed into a substantially true circle and the outer pipe at the connecting portion is formed into an ellipse having a larger diameter in a direction of the partition plate, whereby the clearance is formed between the inner pipe and the outer pipe. Alternatively, the inner pipe at the connecting portion may be formed into an ellipse having a smaller diameter in the direction of the partition plate and the outer pipe at the connecting portion may be formed into a substantially true circle so that the clearance is formed between the inner pipe and the outer pipe.
Further, preferably the inner pipe and the partition plate are formed by a single plate material which is bent substantially into a configuration of an alphabet xe2x80x9cSxe2x80x9d or of a cocoon in cross section.
According to the above-described arrangement, although the partition plate is thermally extended in an amount larger than that of the inner pipe to thereby urge the inner pipe radially outward, the thermal expansion takes place inside the clearance. Therefore, the resistance of the inner pipe against the deformation due to the thermal expansion of the partition plate is smaller and the thermal stress is thus small.
According to another aspect of the present invention, there is provided an exhaust pipe assembly of two-passage and double-pipe construction, comprising: an inner pipe; a partition plate meeting the inner pipe at both diametrical meeting ends thereof so as to be elongated in a longitudinal direction of the inner pipe, whereby two passages divided across a diameter of the inner pipe are formed; an outer pipe covering the inner pipe with a thermally insulating space around a periphery of the inner pipe, wherein the outer pipe has on one longitudinal end thereof a connecting portion for connection with a mating member, and wherein the outer pipe is fixed to the periphery of the inner pipe at a short distance toward a downstream side from the connecting portion while leaving a clearance at the connecting portion between the inner pipe and the outer pipe.
Preferably, the holding portion is formed by reducing a diameter of the outer pipe into close contact with the periphery of the inner pipe. The exhaust pipe preferably further comprises a connecting member provided at the connecting portion which is for connecting the exhaust pipe to the mating member. The inner pipe and the outer pipe at the connecting portion may be formed concentric with each other. Still furthermore, the inner pipe and the partition plate may be formed by a single plate material which is bent substantially into a configuration of an alphabet xe2x80x9cS.xe2x80x9d
According to the above arrangement, the partition plate can be thermally extended into the clearance between the inner pipe and the outer pipe. Further, since the inner pipe and the outer pipe are formed into concentric with each other, the machining is relatively easy.
According to still another aspect of the present invention, there is provided an exhaust pipe assembly of two-passage construction, comprising: an exhaust pipe; a partition plate meeting the exhaust pipe at both diametrical meeting ends thereof so as to be elongated in a longitudinal direction of the exhaust pipe, whereby two passages divided across a diameter of the exhaust pipe are formed; a cover member surrounding a periphery of one longitudinal end of the exhaust pipe, wherein the cover member is fixedly connected to the exhaust pipe at one end of the cover member with a clearance between the periphery of the exhaust pipe and an inner circumference of the cover member, the other end of the cover member and said one longitudinal end of the exhaust pipe forming a connecting portion for connection with a mating member.
Preferably, the cover member is fixedly connected to the exhaust pipe at that end of the cover member which is on a downstream end of the exhaust pipe.
The exhaust pipe assembly preferably further comprise a connecting member provided at the connecting portion which is for connecting the exhaust pipe assembly to the mating member.
Still furthermore, the inner pipe and the partition plate may be formed by a single plate material which is bent substantially into a configuration of an alphabet xe2x80x9cSxe2x80x9d .
According to this arrangement, the exhaust pipe of two-passage construction can be connected to the mating member by means of the cover member while allowing for the thermal expansion of the inner pipe and the partition plate into the clearance between the inner pipe and the outer pipe.